CN1158011A

CN1158011A - Structure and manufacturing process of an aluminum alloy junction self-aligned back-contact silicon solar cell

Info

Publication number: CN1158011A
Application number: CN96114483A
Authority: CN
Inventors: 丹尼尔·L·迈耶
Original assignee: Ebara Solar Inc
Current assignee: Suniwei Co Ltd
Priority date: 1995-11-22
Filing date: 1996-11-15
Publication date: 1997-08-27
Anticipated expiration: 2016-11-15
Also published as: KR970030942A; DE69631815T2; DE69631815D1; ES2216041T3; TW318286B; CN1155106C; CA2181281A1; MX9603156A; CA2181281C; JPH09172196A; EP0776051A3; BR9605346A; EP0776051A2; AU717476B2; US5641362A; AU7063096A; EP0776051B1

Abstract

Solar cell design and manufacturing methods mainly use n-type doped silicon and aluminum to form a pn junction back contact solar cell. The aluminum alloy junction is located on the back of the cell, thus combining the advantages of aluminum with the advantages of a back contact cell. The method includes the following features: surface structuring, front and back surface field minority carrier mirrors, surface passivation, use of aluminum contact electrodes as light reflectors, due to the reverse bias of the adjacent n ⁺ and p ⁺ regions protection, and an improved busbar contact design suitable for interconnecting cells using surface mount technology. To form ohmic contacts, a self-aligned process is used.

Description

A kind of structure and manufacturing process of aluminum alloy junction autoregistration back contact silicon solar cell

The present invention relates to carry on the back the improved design and the manufacture method of contact solar cell.

Except new design, outside new material and the coming of new technology, the evolution of photovoltaic cell is also relevant with all factors.Done a large amount of effort for improving solar energy converting efficient in history, obtained progress is surprising.In 1914, be the illumination of 1 (sunlight is by One Earth One Family atmosphere thickness) for air quality, the efficient of selenium solar cell is 1%, 1954, the efficient of monocrystalline silicon battery reaches 6%, and has arrived the mid-80, and the efficient of solar cell is reported as 22-25%.For using lens or speculum not to increase the concentrator battery of sunlight intensity, it is reported that efficient reaches 27.5%, this almost can compare favourably with the efficient of typical fossil-fuelled power-plants 38-40% and the efficient of light-water nuclear reactor power plant 32-34%.

Yet, for example economical in order to make for the solar cell of the so large-scale application of dwelling house power supply, except efficient, also have other factors to consider.A factor is a production cost of cells.Most of separate houses all have enough roof areas to be used to install the solar cell of traditional design, and the electric energy of 8500 kilowatt hours is provided every year, and this has enough used general family.Yet a coml difficult problem is not efficient but the reduction of unit are solar cell cost.Solve the most promising way of this difficult problem and be to use silicon solar cell, particularly effectively use the battery of thin (about 100 μ m) silicon substrate manufacturing of high quality silicon.Present challenge is the unit price that reduces this solar cell, so that they can be competed with traditional fossil fuel power supply on present energy cost.By improving manufacturing process is to accomplish an approach of this point.

Except manufacturing process, to compare with other design, some project organization is more superior.It seems that one of them be exactly back of the body contact solar cell, especially adopts the back of the body contact solar cell of thin silicon substrates.

Homojunction solar cell has p-n junction, and light induced electron and photohole are separated.In the solar cell of operate as normal, electronics must drive the contact electrode to n section bar material, and the contact electrode to P-type material must be driven in the hole.In semiconductor, optical density is along with the intensification monotone decreasing of the degree of depth, so the preferably close quilt of p-n junction is according to the surface, so that electronics and hole are compound by the separately preceding minimizing of p-n junction.In the thin silicon solar cell, though the thickness of battery is less than the thickness (about 300 μ m) of traditional silicon solar cell, and photon to be transformed into the right possibility of electronics-hole or electric charge-charge carrier less, but the right average life span in light induced electron-hole makes them can be swept to their contact electrodes separately.That is to say that compare with the thickness of battery, the diffusion length of thin silicon solar cell minority carrier is quite long, therefore do not reduce the performance of battery.Among the present invention, minority carrierdiffusion length is equal to or greater than cell thickness.

And in the structure of tradition (just contacting) silicon solar cell, being shone on the surface of battery, big p-n junction is made on the whole substrate.The advantage of this traditional design is simple, because emitter (being generally the P type layer in the p-n junction battery) has covered whole front surface, therefore is not required to be emitter and makes pattern.Yet, front surface in this structure and emission layer are had simultaneously and the requirement of mutual contradiction.On the one hand, in order to reduce take place under the higher-doped concentration compound, the emitter region diffusion should be shallow, and concentration is low (less than 1 * 10 ¹⁹Cm ^-3).On the other hand, the sheet resistance of this light dope, shallow emitter region (cross the top layer of conventional batteries and flow between arbitrary contact grid line (gridcontact line) by the electric current cross-current, sheet resistance and doped layer thickness are inversely proportional to) height, generally greater than 100 Ω/, therefore require the contact grid line closely to arrange, to avoid too much ohm power consumption.

In traditional just contact battery, the solid matter contact wire means the reduction of the energy content of battery, this be since contact material thereunder covering on the silicon cause.In addition, because doping content is low, contact-doped layer interface has rectified action (similar Schottky diode), rather than ohmic contact, causes because the corresponding energy loss that diode turn-on voltage causes.But doping content is high more, and harmful electronics and hole is compound big more in the emission layer, at the near surface that light is injected, and compound maximum.At last, in order to increase capturing of light, the structure that front surface had (texturing) means that contacting grid line must arrange coarse surface and don't lose continuity, and this point is difficult to accomplish.In addition, some structural methods will be difficult to generation more as the porous silicon method and have the inhomogeneity emission diffusion layer of acceptable.

For various reasons, for the conventional batteries structure, must require the heavy doping surface with the formation that promotes ohmic contact and weaken shielding and require the light dope surface with compound and effective the two seeking balance of passivated surface of minimizing charge carrier.The constraint that structuring and shielding cause also is a difficult problem.An alternative method is the back side (non-illuminated area) that p-n junction is placed on battery.In this back of the body contact solar cell, align the requirement and formation p-n junction and formation emitter region of surface structuration and passivation, the requirement of base contact electrode is irrelevant.This means that p-n junction can be darker, can heavy doping and can not bring great consequence in the emitter region.Owing to do not have contact electrode at front surface, being shone lip-deep shielding no longer is a problem, and the spacing of Metal Contact grid line also no longer is a problem.Because the general employing of such battery refers to the type contact electrode again, therefore almost half area on back of the body surface is covered with positive contacting metal, and second half is covered with negative contacting metal.Yet because p-n junction is at the back side of battery, therefore in order to obtain gratifying energy conversion efficiency, the minority carrierdiffusion length in the original material (base) must surpass cell thickness.The best result of this method comes from group of Stanford University, and according to their report, 180 μ m are thick, 35cm ²The zone-melting process back contact silicon battery of area is 1 (100mw/cm at sun irradiance ²) time efficient be 21.3%; 24 ℃ of temperature, air quality 1, sun irradiance is that 1 o'clock efficient is 22% (R.A.Sinton et al., " Large-Area 21%Efficient Si Solar Cells; " Conf.Record 23rd IEEEPhotovoltaic Specialists Conference, P.157 (1993); R.A.Sinton et al., IEEE Electron Device Lett., EDL-7, no.7, p.567 (1986) two pieces all is reference of the present invention).

The manufacturing of the back contact silicon solar cell of people such as Sinton design is quite complicated, involves great expense, and is relevant with the manufacturing of integrated circuit usually.Manufacturing process comprises independent p-type and n-type diffusion (each diffusion all needs to shelter), will bear the contacting metal electrode with photoetching and align with positive contacting metal, and by evaporation and sputtering deposit multilayer contacting metal system, this needs vacuum system.Therefore, though compare with traditional positive contact structures, back of the body contact structures have very big advantage, and the realization of this structure costs dearly.

The present invention only uses the aluminium (Al) of a kind of material-preferably-make back contact silicon solar cell as the ohmic contact material of p-type dopant material and n-type silicon (Si) body layer, therefore reduce the manufacturing cost of silicon solar cell, but still kept quite high solar energy converting efficient.In addition, in a kind of preferred implementation, with a kind of quite cheap silk screen printing of novelty, self-aligned contacts systems approach manufacturing back of the body contact grid line.The distinguishing feature of this contact system is autoregistration, anode oxidation method is applied to a set of contact electrode makes itself and another set of contact electrode isolation, therefore do not need with the mask set version successively accurately centering produce the grid line figure.

In a preferred implementation, the design of back contact silicon solar cell of the present invention also has other several advantages, comprise following but be not limited only to this: surface structuration (in crystal growing process, form and form) with chemical method, front surface and carry on the back surperficial minority carrier mirror, use the surface passivation of silicon oxide layer, the use of antireflecting coating is made the dorsal light reflex device with Ohm contact electrode, adjacent heavy doping n under the negative bias condition ⁺District and p ⁺The interior protection of district's damage, improved negative, positive contact main grid line (contact bus bar) uses when its permission is connected in series battery " surface mounting technology ".

Fig. 1 is the profile of the dendritic band silicon blank of the preferred embodiment for the present invention.

Fig. 2 is the profile that forms positive contact electrode stage band silicon at deposit aluminium.

Fig. 3 is the profile at heat treatment stages band silicon.

Fig. 4 A forms the profile that aluminium oxide is isolated ground floor metal stage band silicon.

Fig. 4 B is the partial enlarged drawing on the band silicon back of the body surface of Fig. 4 A.

Fig. 5 A is from carrying on the back the profile that the band silicon of silica is removed on the surface.

Fig. 5 B is the partial enlarged drawing on the band silicon back of the body surface of Fig. 5 A.

Fig. 6 A is the profile of band silicon when depositing metal forms negative contact electrode.

Fig. 6 B is the partial enlarged drawing on the band silicon back of the body surface of Fig. 6 A.

Fig. 7 is the bottom dorsal view of finished product battery.

Fig. 8 is the plane graph on the back of the body surface of a substrate with 8 batteries.

Fig. 9 is the back of the body surface enlarged drawing of an on-chip battery shown in Figure 8.

Figure 10 is along the sectional view of 10-10 line among Fig. 9.

Figure 11 is used for showing a pair of positive electrode and regional local enlarged detail therebetween.

Figure 12 is the enlarged detail at the top corners place of battery shown in Figure 9.

Now attentiveness is turned to accompanying drawing, a preferred manufacturing process of the present invention and technology have been described here.

Though what Fig. 1-Fig. 7 represented is dendritic band silicon, but should be understood that: as long as the minority carrierdiffusion length of battery under condition of work surpasses cell thickness, the present invention can be applied to any type of silicon, comprise molten (float zone) silicon in district, cut Clusky silicon, magnetic is cut Clusky silicon, fusion (cast) silicon and thin-layer silicon.

The original material of back contact silicon solar cell of the present invention is any n type initial silicon material, is shown in layer 10.The n type dopant that is generally used for silicon is the atom of V group element in the periodic table of elements, comprises lithium, antimony, elements such as phosphorus and arsenic.Yet, should be understood that also battery structure of the present invention is applicable to that also the initial silicon material is the P type, or or even unadulterated because layer 10 effect mainly is as light absorbing zone.

In the preferred implementation shown in the figure, original material (body layer 10 among Fig. 1) is to carry out the dendritic band silicon that the n type mixes with antimony (Sb).Dendritic band silicon is to make the technology cut Clusky silicon and generate with being similar to.Yet, except dendritic band silicon, the also silicon that can use other method to grow, for example zone melting and refining silicon is cut Clusky silicon, molten silicon and thin-layer silicon.The typical thickness of the dendritic band silicon of growth is 100 microns, yet also can adopt other thickness.When thickness was 100 microns, the diffusion length of minority carrier often was 2 or 3 times of cell thickness generally greater than cell thickness.There is n end face and bottom surface at antimony doping silicon ribbon ⁺ Thin layer 20, they diffuse into two surfaces and generate when band silicon is still in growth furnace.If in band silicon growth process, do not form n ⁺ Superficial layer 20 also can form with any feasible process beginning to add man-hour, comprises by quick thermal treatment process with liquid doped source simultaneously to front and back side diffusion.n ⁺Layer produces " surface field ", makes the hole leave the surface, has reduced surface recombination there, and p-n junction is quickened to arrive in the hole that produces at superficial layer, and surface field also helps short circuit current and open circuit voltage increases, and has strengthened solar energy converting efficient thus.The n at the back side is arranged again ⁺Layer helps the ohmic contact of negative contacting metal, and this also will tell about below.

In addition, all structurings of end face and bottom surface, purpose is to catch more incident light.Can grow out as this structure with sawtooth pattern 30 expressions among the figure, can generate porous silicon layer by the anode etching introduces (as the method for people such as Y.S.Tsuo description, " Potential Applications ofPorous Silicon in Photovoltaics ", Conf.Record 23rd IEEE PhotovoltaicSpecialists Conf. (Louisville, KY) (1993), as reference of the present invention), or introduce by mechanical means saw or optical means such as laser ablation.Though in a preferred embodiment, structure and doping surfaces are expressed out, and generally, their application is optional.In addition, for clarity sake, the structuring of battery bottom surface does not show in Fig. 2-Fig. 6.

Fig. 1-Fig. 6 has illustrated the important step in the solar cell manufacture process, comprise with aluminium not only as dopant but also as the ohmic contact material, and aluminium what shelter usefulness is the autoregistration anode oxidation process.Aluminium here or aluminum refer to fine aluminium or the silicon concentration aluminium-silicon alloys less than eutectic component (weight ratio is 88.7% aluminium and 11.3% silicon).On nearly half area on whole back of the body surface with strip deposit aluminium, the wide 100 μ m of each aluminum strip bar, the about 100 μ m of the distance between the aluminum strip edge are shown in spacing among Fig. 2 40.In order effectively to collect charge carrier, the distance 40 between the aluminum strip 50 should be less than the diffusion length in minority carrier (hole).Bar wide and the distance also can be reduced to below the 100 μ m, to obtain some benefit.The wide higher limit of useful bar is about 2000 μ m, and useful aluminum strip edge spacing 40 scopes are about 50 μ m to 300 μ m.Like this, each bar all forms the independently doped source material sections as the p-n junction solar cell in the aluminum strip in parallel, and the base that can further be interpreted as these isolated areas here links together, and forms as the main grid line district that just contacts the main grid line.

In preferred aluminium deposition process, with technical known silk-screen printing technique own with aluminium paste state deposit aluminium.Aluminum strip is shown in Fig. 2, and aluminium is deposited into the form of the aluminum strip 50 that enters paper herein.Therefore yet other deposition process except silk screen printing also belongs in the scope of the present invention, as electron beam evaporation and sputter, though these methods need more expensively owing to photoetching, is not used very much.

Generally speaking, compare with n type body layer, the aluminium lamination of p section bar material is quite thin, thick 2 to the 20 μ m of aluminium lamination during the about 100 μ m of body bed thickness.

Attention is in preferred implementation of the present invention, select aluminium to be used for three purposes at least simultaneously: as p type doped source, as positive contacting metal, and the part back of the body surface light reflector of the back of the body surf zone that is covered with as it, it is covered with the area on back of the body surface about 50%.

Note now seeing the heat treated Fig. 3 of explanation, it expresses the result of aluminium lamination after heat treatment under about 850 ℃ of oxygen-enriched environments of deposit.In this step operation, form p-n junction with silicon alloy by the aluminium in the silk screen printing.Under 850 ℃, further keep extra a period of time, for example 30 minutes or longer, can help forming gratifying alloy.Temperature range can be from 577 ℃ in aluminium-silicon eutectic point to silicon 1420 ℃ of fusing points.Can use fast heat treatment device, band oven, tube furnace or miscellaneous equipment heating.The also available inert gas of surrounding environment, for example argon gas or nitrogen, or use chemical reaction gas, as oxygen or hydrogen.The also mixture of available environmental gas.Heating-up time can be from 30 seconds to several hours.In a preferred embodiment, wish to adopt oxygen-enriched environment under this temperature, this can make the oxide layer (SiO that grows on any exposed silicon ₂), make surface passivation and reduce harmful composite action.

The silicon-aluminum alloy temperature is reduced, utilize liquid phase epitaxy regeneration silicon, reduce to eutectic point (577 ℃) up to temperature.Result's silicon of regenerating is used aluminium (about 10 now ¹⁸Cm ^-3) mixing becomes the p type, as p among Fig. 3 ⁺Layer 60.When aluminum concentration surpasses the donor concentration of initial silicon, form desired p-n junction, eutectic alloy (weight ratio is about 88.7% aluminium, 11.3% silicon) still is present in the surface, as with the contact electrode of P type silicon.Be to be noted that because p-n junction at absorbing light cell backside seldom, is compared with traditional solar cell that just contacts, and junction depth is less important, thus p-n junction can do quite dark (downward 1 to 20 μ m) from the surface.When silk screen printing, can control the alloy junction junction depth and do deposition materials without fine aluminium with aluminium-silicon mixture.Reason is the increase along with silicon concentration in the eutectic composition, and the silicon amount that typographic metal can dissolve reduces, so junction depth shoals.If desired, by the thickness of the aluminium in the increase deposit and according to aluminium-silicon phasor raising alloy temperature junction depth is deepened.

In addition, because the characteristic of dendritic band silicon (preferred silicon kind of the present invention), under nearly 850 ℃ of temperature, the defective that any quenching is fixed up, for example silicon room and self-interstitial defective are removed by annealing, and the silicon body minority carrier lifetime may increase.Compare with fast cooling, lowering the temperature with the controlled rate of 10 ℃ of per minutes also to make the Si defective that is fixed up of quenching remove through annealing, has reduced harmful spot.

Above-mentioned Technology for Heating Processing can realize that in band oven, sample is placed on the conveyer belt with band oven, and conveyer belt was slowly dragged the flat-temperature zone in the stove.As an alternative, in such stove, silicon/aluminium mixture was heated about 30 minutes down at 850 ℃.Also available various other technology forms silicon/aluminium eutectic, for example use fast heat treatment device, it for example utilizes that quartz lamp is heated to 1000 ℃ with silicon, and keeps this temperature 30 seconds, this can increase the production capacity under the business contexts, for example uses traditional quartz tube furnace again.

This p ⁺Direct and the n in district (zone 60 among Fig. 3) ⁺The district is in the adjacent advantage that also has unanticipated of back of the body superficial layer (back of the body superficial layer 20 among Fig. 1): during when the solar cell reverse bias, it is overheated for example to prevent during crested in assembly.One " assembly " is one group of interconnection battery with glass or the protection of other cladding material, and when being subjected to illumination, it can produce a large amount of electric energy, and representative value is 10 to 100 watts.This p ⁺n ⁺Design have built-in to back-biased defence, make and need not be constructed for preventing reverse bias alleged " bypass diode " usually.This p ⁺n ⁺The effect of knot is similar to Zener diode, and it only needs very little voltage to puncture under suitable reverse biased, and only therefore consuming cells power consumption has seldom protected battery.

Note 4A with the aid of pictures and Fig. 4 B now, it has illustrated another operation in the preferred implementation of the present invention.This operation has unique " autoregistration " characteristic, is used for negative contact electrode (to n type district) with respect to positive contact electrode (to p type district) centering.For p type layer contact electrode (positive contact electrode) and n type layer contact electrode (negative contact electrode) are kept apart, the mask technique of the complexity used is not adopted over always in the present invention, but cover first group of (just) aluminium contact electrode, and this group is kept apart with second group of (bearing) contact electrode electricity by forming oxide layer.Exist under the environment of oxygen, by at exposed silicon, on silicon-aluminium and the aluminum with Al ₂O ₃, SiO ₂, or the oxide layer 80 (insulator) that certain mutation form forms naturally is with aluminium-silicon p ⁺Composition of layer and the aluminum strip 70 that is exposed to band silicon blank 10 outsides are kept apart and are accomplished above this point, shown in Fig. 4 A and Fig. 4 B.It is thick that the oxide layer of covering aluminum strip 70 should be grown about 0.1 μ m to 1 μ m.Shown in Fig. 4 A and Fig. 4 B, in this step operation, oxide layer 80 has also covered the n laminar surface zone 90 between the aluminum strip 70.For the negative electrode (n type silicon) that can make ohmic contact regions energy and solar cell diode forms ohmic contact, the oxide layer on the surf zone 90 then will be removed (operation shown in face Fig. 5 B as follows), and this also can describe in detail below.

The method for optimizing that forms oxide layer in Fig. 4 A and Fig. 4 B is anodic oxidation, and in the time of in this way, the superficial layer of processed battery is dipped in the weak electrolyte (as borate, phosphate or carbonate) and applies voltage.Owing to applied voltage, between chemically inert electrode and contacting metal (aluminium-silicon eutectic), had electric current to flow through.Reach to 700V (14 dusts/V or 1.4nm/V) if drive the voltage of oxidation current, then the thickness of anodic oxide coating can reach 1 μ m.This oxide layer is fine and close and do not have a pin hole.Owing to make Ohm contact electrode must for contact main grid line (shown in the zone 110 among Fig. 7) intact man-hour at photocell, thereby make contact electrodes for exposed aluminum strip 70, so must forbid generating anodic oxide coating (this main grid line district in the anodic oxidation operation must conductively-closed) in main grid line district.A kind of compression of a kind of method of doing like this, however be that the shared area of medium and main grid line of conduction contacts, and for example usefulness is soaked the closed pore sponge of carbon.Because closed pore sponge Electolyte-absorptive not, therefore the most handy it.

Except anodic oxidation, the present invention can adopt any other method that is used for isolating aluminium or aluminium-silicon eutectic layer, for example aluminium oxide in containing oxygen plasma.

In that to generate oxide layer by anodic oxidation or other suitable method after 80s, in order to make negative contact metal layer aluminium deposit thereon, the n type silicon face at the surface region 90 in aluminum strip gap that is covered with oxide layer must come out.Like this, referring to Fig. 5 A and Fig. 5 B, they have illustrated how oxide layer is removed from the silicon layer of carrying on the back the surface, and do not remove the oxide layer that covers on the aluminum strip 70.The method for optimizing of accomplishing this point is with hydrofluoric acid etching and remove SiO in the gap optionally ₂(silicon dioxide) 20 is because hydrofluoric acid discord Al ₂O ₃(aluminium oxide) works, thereby Al ₂O ₃Can not remove.As a result, the SiO in the gap ₂Be removed, and cover Al on the aluminum strip contact electrode 70 ₂O ₃Insulating barrier still keeps, referring to Fig. 5 B.Also available other has the chemicals of similar effect, or with the technology of other deoxidation layer, for example use weak sand milling (lightsandblasting) method of silicon dioxide layer, this method also has the benefit that makes the weak damage of silicon chip surface that exposes, and this is of value to the ohmic contact with n type base.Used weak sanding method just needn't form n at the back side of battery ⁺Diffusion layer 3 is used n ⁺Diffusion layer mainly also is to benefit ohmic contact, and also available reactive ion etching (RIE) is removed SiO ₂And reservation Al ₂O ₃The also available weak injured surface of ion milling that is similar to sand milling is beneficial to ohmic contact.

Fig. 6 A and Fig. 6 B have illustrated next step operation in the solar cell manufacture process of the present invention, promptly form the negative metal ohmic contact (for the contact of n type silicon layer) of autoregistration with the second layer metal layer.This second layer metal can be any suitable contacting metal, comprises aluminium and silver.Silk screen printing also is the method for optimizing of this second layer metal of deposit, also can adopt other method such as for example electron beam evaporation or sputter etc.This second layer metal layer that is expressed as metal level 100 has almost covered the whole back side of battery.By anodic oxide coating 80 this second layer metal and ground floor Metal Contact bar 70 isolated, and the n of 70 of this second layer metal and the bonding jumpers that form by ground floor deposit aluminium lamination ⁺District 90 forms ohmic contact.The second layer metal layer also helps to form back of the body surface light reflector, will be for the first time by silicon materials the time in the unabsorbed light reflected back silicon materials.

Fig. 7 represents the solar cell of the completion seen from the back side, is covered with second layer metal (aluminium or other ohmic metal) or aluminium-silicon eutectic on the battery.This solar cell of the present invention has one without any the front surface that blocks, and compares with traditional solar cell, and this is a great advantage.Overleaf, two metal contact layers (ohmic metal contact layer 70 and 100) also play the local light reflector except as the ohmic contact layer.In addition, since the outside that the design need not make inconvenience just-anti-internal element contact (external front-to-back inter-cell contacts), and use more " mounted on surface " technological designs that do not need this contact, therefore the design of the main grid line of solar cell of the present invention makes battery be interconnected as the form of serial connection simply.

Referring to Fig. 7, wherein expressed main grid line district 110, it is zoneofoxidation not, as previously described, the main grid line contacts from leading to the positive contacting metal bar of ground floor 70a here.Main grid line district 110 seems may be littler than the area that is covered by negative contact metal layer 100, but positive Metal Contact district and negative Metal Contact district the two all be of value to the mounted on surface design of assembly type.Aluminium-silicon eutectic interdigital 70 stretches away from the main grid line 110 of Fig. 7 vertically upward, but owing to be covered with by second layer metal 100, therefore cannot see in the drawings.

If desired, also can deposit other metal ohmic contact except aluminium or silver positive and negative ohmic contact regions of forming here to be said, for example use titanium/palladium/copper three-decker or silk screen printing silver as contact layer.

About using antireflective coating (AR), the outermost at the front surface of quilt photograph has one deck or which floor antireflective coating usually, but for the sake of clarity, does not show among Fig. 1-Fig. 7.For the design, the AR film may be optionally, as mentioned above, because structuring or structuring are enough to play antireflecting effect with combining of passive oxidation layer, does not therefore need antireflective coating.Yet, can use by the silicon nitride antireflective coating of plasma reinforced chemical vapor deposition (PECVD) generation or the titanium dioxide antireflective coating of apcvd (APCVD) generation.If the surface does not have oxide layer to exist or oxide layer is extremely thin, before deposit AR film, also can carry out hydrogen ion and inject (being used for improving minority carrierdiffusion length).

What Fig. 8 represented is with cutting aluminum alloy junction interdigitated back of the body contact (IBC) solar cell 120 that the Clusky silicon chip is made as initial substrate.These batteries are used for illustrating the use of aluminum alloy junction in the back of the body contact structures.Aluminium is by electron beam evaporation rather than by in the silk screen printing deposit.Negative electrode is not self aligned with anodic oxidation or other technology, but the contact centering equipment of using with the manufacturing integrated circuit with negative electrode with respect to aluminium-artificial centering of silicon eutectic positive electrode.

Silicon substrate film is a single-sided polishing, 3 inches of diameters, and the 13-17 mil thick, phosphorus doping uses (111) face to 3-20 Ω-cm.Processing test structure and solar cell on two slice, thin pieces burnishing surface of (representing) with CZ-7 and CZ-8.What Fig. 8 represented is the back side of one of them slice, thin piece.Front surface (can't see among Fig. 8) has phosphorus-diffused layer and antireflective coating (AR) 95 (seeing Figure 10 and Figure 12).Each that does not include as wide 112, eight solar cells of main grid line of the wide 2mm of negative electrode all is 1 square centimeter big.These eight batteries below table 2 and table 3 in the n that forms negative contact electrode ⁺(inner (I) or peripheral (P)) represents in the position of interdigital number (4,8,16 and 25) and battery.Four are positioned at inner battery and have only eutectic alloy and p ⁺District contact, and be deposited with second layer metal on four eutectic alloys that are positioned at outside battery.The result that the CZ-8 sheet obtains is better, so only narrate the technology and the test result of this slice, thin piece.

Be used to make the process summary such as the following table of the CZ-8 sheet of IBC battery.The aluminum alloy junction that noticeable characteristics of this technology are the back side and at whole front surface and exposed back of the body surface forms between the aluminium electrode phosphorus doping n ⁺The shared high-temperature process of layer finished.The figure that carves the aluminium in the evaporation with photoetching reaches the second layer metal location of giving as negative electrode.Fig. 9 is the back view of this aluminum alloy junction IBC solar cell, and Figure 10-Figure 12 is its sectional view.

Table 1

Figure (mask 1) AZ1350J 1.5 μ m spraying, band oven are made in manufacturing process in-process capacity materials thickness technology 1 deposit aluminium (at burnishing surface) the Al 3 μ m evaporation 2 of CZ-sheet

Baking 3 go aluminium Al 3 μ m carve aluminium 4 in the front and the back side (on the aluminium) P-507 0.3 μ m print liquid doped source

Coating liquid phosphorus doped source 5 generates p overleaf ⁺District Al 3 μ m rapid thermal treatment

(alloy) reaches at the positive and back of the body 0.3 μ m (1000 ℃, 30 seconds)

Look unfamiliar into n ⁺District P-5076 makes figure (mask 3) AZ1350J 1.5 μ m rotation, heating plate

Toasting 7 depositing metals (at burnishing surface) Ti/Al, 500 dusts/0.5 μ m evaporation 8 makes contact electrode n/a n/a and divests 9 protection front side diffusion layer waxes and melt silicon n between the 10 etching electrodes with heating plate arbitrarily ⁺50: 1 HNO of Si 1.5 μ m ₃: HF,

2 minutes 11 coating antireflective coating TiO ₂The rotation of 750 dusts

(2500rpm, 30 seconds) 12 baking antireflective coating TiO ₂450 ℃ of 750 dusts, air

Some explanations of relevant CZ-8 technologies:

Alloy/n ⁺Diffusion technology is included in the progressively temperature-fall period (about 50 ℃/minute are reduced to 825 ℃ from 1000 ℃) in quick thermal treatment process (RTP) equipment;

Form p simultaneously at quick thermal treatment process with 1000 ℃ ⁺And n ⁺On aluminium, print liquid phosphorus doping source before the district and do not have tangible harm;

For 1000 ℃, 30 seconds quick thermal treatment process is measured the p that section draws with ESEM ⁺District's degree of depth is 5 μ m;

1000 ℃, the n that measured after the rapid thermal treatment in 30 seconds ⁺The sheet resistance of front surface is 25 Ω/;

Do not use mask 2, because just some resolution chart need be used it, the IBC battery need not;

Divesting technology restriction n ⁺Titanium/the aluminium of surface contact is thick to be 0.55 μ m;

Between positive electrode (eutectic) and negative electrode (titanium/aluminium) if there is not an etching n ⁺Silicon, p-n junction can be by bypass seriously.

Illumination (AM1.5,100mW/cm before the table 2 coating antireflective coating ², the front lighting photograph) and following I-V data slice battery numbering Jsc Voc fill factor, curve factor efficient

(mA/cm ²) (V) ％ CZ-8 4I 22.4 0.516 0.611 7.07 CZ-8 8I 19.9 0.522 0.621 6.45 CZ-8 16I 19.6 0.518 0.581 5.90 CZ-8 25I 20.6 0.510 0.580 6.08

Illumination (AM1.5,100mW/cm behind the table 3 coating antireflective coating ², the front lighting photograph) and following I-V data slice battery numbering Jsc Voc fill factor, curve factor efficient

(mA/cm ²)?(V) ％ CZ-8 4I 27.6 0.515 0.635 9.01 CZ-8 8I 24.2 0.515 0.691 8.61 CZ-8 16I 23.6 0.510 0.695 8.35 CZ-8 25I 23.5 0.505 0.716 8.50

Note the usefulness that back of the body contact solar cell is obtained, thereby showed the life-span of described structure.The light that measures-electric energy conversion efficient is up to 9%.Expectation further improves basis material and processing technology, so that efficient is brought up to one times as the present efficient that proves.

Although below comprehensively, intactly introduced preferred implementation of the present invention, yet can also adopt various improvement, alternative structure and equivalents.For example, form diffusion of P type and Ohm contact electrode with aluminium although described preferred implementation always, however other III family metal, and for example gallium and indium all can be used for this purpose.Suitable III family element can dissolves silicon, and preserves therein when silicon solidifies and become dopant on a small quantity.In addition, though use n type body silicon layer 10 when describing preferred implementation always, also available p type body silicon manufacturing back of the body contact solar cell.During with p type body silicon layer, form a p at end face ⁺ Thin layer 20, but n formed in the bottom surface of body layer 10 ⁺Layer.In p type execution mode, minority carrier is an electronics, and the person skilled in the art values this point very much.Therefore scope of the present invention is not limited only to above description and explanation, will limit scope of the present invention in the additional claims.

Claims

1. Back contact solar cells, including:

a semiconductor body layer of the first conductivity type having a front surface and a back surface;

a plurality of spaced apart doped semiconductor regions of opposite conductivity type formed in said bulk layer adjacent to said back surface and a plurality of semiconductor junctions formed therefrom;

a first set of spaced apart ohmic contact electrodes arranged along said back surface and connected to said plurality of spaced apart doped semiconductor regions;

a second set of ohmic contact electrodes connected to said back surface of said bulk layer in the gaps between said first set of ohmic contact electrodes; and

Insulation means for electrically isolating said first set of spaced apart ohmic contact electrodes from said second set of ohmic contact electrodes.

2. The solar cell according to claim 1, wherein said first set of ohmic contact electrodes are in the form of conductive strips substantially parallel to each other.

3. A solar cell according to claim 2, wherein said conductive strips are connected together at one end to form a busbar contact.

4. The solar cell according to claim 1, wherein the thickness of said semiconductor body layer does not exceed the diffusion length of minority carriers of said first conductivity type.

5. The solar cell of claim 1, wherein said bulk layer is n-type silicon.

6. The solar cell according to claim 5, wherein said n-type silicon is dendritic band silicon.

7. The solar cell of claim 1, wherein said first set of spaced apart ohmic contact electrodes is formed from an alloy of said bulk layer semiconductor material and a Group III metal comprising a group III metal for said A plurality of spaced apart semiconductor regions doped with acceptor dopants.

8. The solar cell according to claim 7, wherein said group III metal is selected from the group consisting of aluminum, gallium, indium.

9. The solar cell of claim 1, wherein said insulating means comprises an insulating layer covering the first set of ohmic contact electrodes.

10. The solar cell according to claim 1, further comprising an anti-reflection film on the front surface.

11. The solar cell according to claim 1, wherein said bulk layer is composed of n-type material, and said front and back surfaces are initially n ⁺ doped.

12. The solar cell of claim 1, wherein said second set of ohmic contact electrodes is composed of an ohmic metal selected from the group consisting of silver, aluminum, copper, titanium and palladium.

13. The solar cell of claim 1, wherein at least one of said front or back surfaces is structured to increase light capture by said bulk layer.

14. A method of fabricating a back contact solar cell with self-aligned ohmic contact electrodes comprising the steps of:

(a) providing a semiconductor body layer of the first conductivity type, said body layer having a front surface and a back surface;

(b) forming a plurality of semiconductor diffusion regions of opposite conductivity type in said bulk layer of said back surface;

(c) forming a first set of spaced apart ohmic contact electrodes on said back surface with ohmic contact metal material for said diffusion regions;

(d) electrically insulating said first set of ohmic contact electrodes at the gap therebetween; and

(e) forming a second group of ohmic contact electrodes in said gap on said back surface with ohmic contact metal material, said second group of ohmic contact electrodes being electrically insulated from said first group of ohmic contact electrodes of.

15. The method for manufacturing a back contact solar cell according to claim 14, wherein n-type silicon is provided in the step (a).

16. The method for manufacturing a back-contact solar cell according to claim 14, wherein said step (a) provides n-type silicon with an n ⁺ surface diffusion layer on the front surface.

17. The method for manufacturing a back-contact solar cell according to claim 14, wherein in said step (a), n-type silicon with n ⁺ surface diffusion layers on both the front surface and the back surface is provided.

18. The method for manufacturing a back contact solar cell according to claim 14, wherein said step (b) and step (c) are performed simultaneously.

19. The method for manufacturing a back contact solar cell according to claim 14, wherein said steps (b) and (c) are carried out simultaneously: on the group III metal layer on the back surface of said body layer patterning, heating the back surface and the inner region adjacent to said bulk layer, at least forming an alloy between the bulk material in said inner region and said patterned Group III metal layer, and then allowing the alloy to cool, The diffusion region formed by the group III metal is made acceptor doped, and the cooled alloy remaining on the back surface forms a first set of contact electrodes.

20. The method of manufacturing a back-contact solar cell according to claim 19, wherein said patterned layer is composed of a mixture of Group III metal and bulk layer material.

21. The method of manufacturing a back contact solar cell according to claim 20, wherein said mixture is composed of aluminum and silicon.

22. The method of manufacturing a back contact solar cell according to claim 19, wherein said patterned layer is composed of a plurality of individual strips.

23. The method of manufacturing a back contact solar cell according to claim 22, wherein said strips are substantially parallel to each other.

24. The method of manufacturing a back-contact solar cell according to claim 19, wherein said layer on which the pattern is made is made by screen printing.

25. The method for manufacturing a back-contact solar cell according to claim 14, wherein said electrical isolation step (d) is performed by forming a an insulating layer, and selectively removes that portion of said insulating layer in said space from said back surface of said body layer, so that said insulating layer substantially only covers said first A set of ohmic contact electrodes, while the gap is exposed.

26. The method of manufacturing a back-contact solar cell according to claim 25, wherein said step of selectively removing comprises a step of etching said part of said insulating layer on said gap.

27. The method for manufacturing a back-contact solar cell according to claim 26, wherein said etching step is chemical etching.

28. The method of manufacturing a back contact solar cell according to claim 26, wherein said etching step is reactive ion etching.

29. The method of manufacturing a back contact solar cell according to claim 25, wherein said step of selectively removing comprises a step of sanding said insulating layer on that part of said gap.

30. The method of manufacturing a back contact solar cell according to claim 25, wherein said step of selectively removing comprises a step of ion milling said insulating layer on said part of the gap.

31. The method for manufacturing a back-contact solar cell according to claim 14, further comprising a step of structuring at least one of said front surface and said back surface on said bulk layer.

32. The method for manufacturing a back-contact solar cell according to claim 14, further comprising a step of coating an anti-reflection film on the front surface.